Signaling circuits for toll lines



I. DAVIDSON, JR.

SIGNALING CIRCUITS FOR TOLL LINES.

APPLICATION FILED DEC. 12, ms.

.1 429 9 3 1 I Patented Sept. 26, 1922.

8 SHEETS-SHEET I.

' TOO/0113' Set ITTT'I I N VEN TOR.

ATTORNEY 1. DAVIDSON, JR- SIGNALING CIRCUITS FOR TOLL LINES.

APPLICATION FILEDDEC. I2, 19I8.

1,429,931, I PqtentedSept. 26, 1922 8 SHEETS SHEET 2.

ATTORNEY J. DAVIDSON, JR-

SIGNALING CIRCUITS FOR TOLL LINES.

APPLICATION nu-zn 020.12.1918.

Patented Sept. 26, 1922. v

8 SHEETS-SHEET 3- lull I 108 IN VEN TOR.

ATTORNEY 1. DAVIDSON, 1n. SIGNAUNG CIRCUITS FOR TOLL LINES.

' APPLICATION FILED DEC. l2, 19l8. 1,429,931.

E QQQ IN VEN TOR. Jfiavmkomfi: BY c;

ATTORNEY J. DAVIDSON, IR.

SIGNALING CIRCUITS FOR TOLL LINES.

APPLICATION FILED DEC. 12, I918.

Patented Sept. 26, 1922. a SHEETSSHEET 5.

'INVENTOR. Jflamiwgfi BY -W A TTORN E Y I. DAVIDSON, In. 1

SIGNALING CIRCUITS FOR TOLL LINES.

I APPLICATION FILED DEC. I2, I918.

Patented Sept. 26, 1922,

8 SHEE]'SSHEET 6.

vv mi C if I'VEN TOR.

ATTORNEY I. DAVIDSON, In. I SIGNALING CIRCUITS FOR TOLL LINES.APPLICATION men 050.12.19ua.

1,429,931, PatentedSept. 26, 1922 8 SHEETS-SHEET 1.

IIIIII IN VEN TOR.

A TTORNEY 1. DAVIDSON, .ln.

SIGNALING CIRCUITS FOR TOLL'LINES. APPLICATION FILED 050.12.1918.

1 ,429,93 1 v Patented Sept 26. 1922.

8 SHEETS-SHEET 8.

To L

I V g 05 INVENTOR.

J. fizz/01223012, J: BY

ATTORNEY Patented Sept. 26, 1922.

UNITED STATES 1,429,931 PATENT OFFICE.

JOHN DAVIDSON, JR., 0F MON'I'CLAIR, NEW JERSEY, ASSIGNQR TO AMERICANTELE- PHONE AND TELEGRAPH COMPANY, A CORPORATION OF NEW YORK.

SIGNALING CIRCUITS FOR TOLL LINES.

Application filed December 12, 1918. Serial No. 266,487.

T 0 all whom it may concern:

Be it known that I, JOHN DAVIDSON Jr., residing at Montclair, in thecounty of Essex and State of New Jersey, have invented certainImprovements in Signaling Circuits for Toll Lines, of which thefollowing is a specification.

This invention relates to signaling circuits and more particularly tosignaling circuits for use in connection with long distance telephonelines.

One of the objects of this invention isto provide a toll lineterminating at an oflice at a plurality of positions and so arrangedthat an operator at a different oflice may signal anyone of thepositions. Another object of the invention has reference to theprovision of a two way toll line so designed that connections may beestablishedthereover in either direction. A further object of theinvention has reference to the provision of a toll line of suchcharacter that when a connection is established over two or more of suchlines in tandem, the orginating operator has complete control over theconnection, independent of any intervening operators who may have takenpart in setting up the connection. A still further object of theinvention is to provide signaling arrangements for toll lines, suchthatwhen a connection is established over two or more of such lines intandem, signals originatingat the distant end of one of the lines willbe transferred by the connecting means of the lines to the distant endof the next line connected thereto. The invention also hasfor one of itsobjects, the provision of a link circuit for connecting two toll linesin tandem, the link circuit being so arranged that when the connectionis once established the tandem operator will beautomatically preventedfrom listening in or interrupting the connection by means of hercontrolling keys. Other and further objects of the invention will beclear from the detailed description hereinafter given.

The objects of this invention are secured, as herein disclosed, byproviding a plurality of toll lines, each of which terminates at eachend at a plurality of positions. At one of these positions, hereinaftercalled the outgoing position an outgoing toll operator may initiatecalls which are to be eX- tended over the line. At anotherof thesepositions, hereinafter called the incoming position, an incoming tolloperator may complete the local calls coming in over the long distanceline. At another of these positions, hereinafter referredto as thethrough position, a through toll operator may complete connectionsincoming from one toll line to another toll line, thereby extending theconnection to-a distant station.

In order that an originating operator may select any one of thepositions at the distant end of the toll line, such an operator isprovlded With an outgoing jack corresponding to each of the positions atthe distant stat on. By plugging into the proper jack, s gnallngequipment is set into operation, whereby a lamp is lighted at theparticular position desired. In order that the signaling operations thusrequired may be performed economically, a signaling path is providedwhich is common to a plurality of toll lines and over which the varioussignals incidental to the establishment of connections over a pluralityof lines may be successively transmitted, The arrangement forsuccessively transmitting the signals over a common path may be of thegeneral type disclosed in United States patents to Bancroft Gherardi,Numbers 1,251,363 and 1,251,864, granted December 25, 1917. As hereindisclosed, however, the apparatus of the said Gherardi patents ismodified so as to permit of transmitting. one or more code combinationfor each of the t-oll lines, said combinations corresponding'todifferent signals. The use of code combinations to transmit thedifferent signals, readily permits of the selection of differentpositions at distant stations since 1 each position may havea particularcode combination assigned to it. The apparatus for translating thesignals into code combinations and for translating the code combinationsinto signals at the distant station is herein illustrated as being ofthe same type as that disclosed and claimed in patent No. 1,413,708,issued April 25, 1922.

In order that the originating operator may have entire supervision overall connec tions, whether extended over a single toll line or over aplurality of toll lines in tandem, a toll .cord is provided, of suchcharacter that when it is used for originating connections the operatormay. at any time come in upon the connection for any purpose whatsoever,but when used; at an incoming or through position for completing and shewill be unable thereafter to listen in or interfere with the connectionexcept for the purpose of taking down the connection upon receiving adisconnect signal. Since the originating toll operator'is-to have entiresupervision of the connection, some arrangement must. be providedwhereby the signals transmitted over a signaling path to the distant endof a toll line may be repeated or otherwise extended over the succeedingtoll line connected in tandem therewith. This result is accomplished byproviding the toll cord with signal responsive means adapted to beactuated by signals incoming from one toll line and arranged to controlsignal initiating apparatus whereby similar signals may be transmittedover thesignaling path for the succeeding toll line.

The invention may now be more fully understood from the followingdescription when read in connection with the accompanying drawings,Figures 1 to 8, inclusive, of which, when taken together, constitute acircuit diagram ofapreierred embodiment of the invention. In order thatthe drawing may be more clearly read the sheets should be arranged withFigures 1, 2, 3 and i arranged end to end, and Figures 5, 6, 7 and Slikewise placed end to end and below the first tour figures.

Referring to the drawing, a toll line L, is shown extending between twodistant stations M and N. At each station the toll line terminates in anumber of jacks and associated signaling equipment, the apparatus ateach'station being identical. In order to establish connections betweena local line and a long distance toll line, or between two long distancetoll lines, toll cords, such as TC and TC, may be provided at theterminating stations of the toll line. The toll cord TC at station Mterminates in plugs PM and PM. The plug PM is adapted to co-operate withany one of a plurality ot jacl s, 007 0J1, OJ TAILJO, A A-J1 Byinserting the plug PM in the jack O-l a connection will be extended overthe toll line and a lamp associated with the answering jack AJ at theoutgoing board of the distant station will be lighted, thereby callingthe attention of the outgoing operator. By inserting the plug PM in thejack l-l, a lamp associated with the answering jack AJ, at the incomingboard of the distant station will be lighted. Likewise. by inserting theplug PM in the outgoing jack Gil a lamp associated'with the answeringjack AJ, at the through operators station will be lighted. The plug PMmay also be inserted in any oi? the answering jacks AJO,

AJ, or AL, in answering incoming calls ex tended from the distantstation by inserting the plug PN of the toll cord TC at that stationinto some one of the outgoing jacks 0J OJ, or OJ The plug PM of the tollcord TC may be usedin connection with a toll switching trunk, such as T,from a local line, or said plug may be inserted in the jack of a longdistance line over which a connection is to be established in tandemwith the line, such as L In a similar manner, the plug PN of the cord TCat station N may be used for connections extended in the oppositedirection.

In order that signals may be transmitted for selectively lighting thelamps at the incoming board and for performing the various othersignaling operations incidental to the establishment of a connection, asignaling path P, extending between the two stations M and N, isprovided, said signaling path being common to a plurality of toll lines,such as L extending between said stations. Said signaling pathterminates at the distant stations in bridged polar duplex sets of thetype commonly used in duplex telegraph systems. Since the commonsignaling path is to be used for transmitting signals of a plurality oftoll lines, some arrangement must be provided whereby the signals of aplurality of lines will be sent in succession and in predeterminedorder. For this purpose, a pair of relays G and H are associated withthe line L at station M, similarrelays G and H being associated with theline at station N. All of the other lines signaling over the path P areprovided with similar relays at the two stations. These relays performthe triple function of preventing the transmission of more than onesignal at a time, of determining the order in which the signals of lineswhich are simultaneously in signaling condition shall be transmitted andof translating the signals ,into code combinations to be transmittedover the signaling path. The H relays associated with the lines are soarranged that they remain locked up after the signal of thecorresponding line has been transmitted, thereby determining thatsignals of waiting lines shall be trans mitted in numerical orderbeginning with the line whose H relay is nearest on one side of the Hrelay of th line last signaled. As soon as new line obtains control ofthe circuit, the H relay of the previous line is unlocked and released.

In order to transmit the code combinations determined by the relayarrangements above described, an intermittently operating'transmittingdistributor TD is associated with the signalingpath P at the fortransmitting from station it to station N, and an intermittentlyoperating receiving distributor RD is associated with the station M bestunderstood from a this circuit.

signaling path P at the station N for receiving the transmitted codecombinations. Similarly, transmitting distributor TD and receivingdistributor RD are provided at stations N and M, respectively, for 1code combinations transmitted in the opposite direction. Thesedistributors are similar to the so called start-stop distributors usedin connection with printing telegraph systems. In order to translate thereceived code combinations into signals and to appropriate the signalsto the proper toll line, pyramid relay combinations, illustrated inFigures 6 and 7, are provided at stations M and N, re spectively.Various circuit controlling relays are also associated with the tolllines at the two stations for controlling the circuit changes resultingfrom the various signals.

In order that a signal originating with a given toll line, extendingfrom one station to another, may, when arriving at the distant stationbe transmitted from that station to still another station, to which atoll line connected in tandem with the first mentioned toll lineextends, the toll cords for connecting the toll lines in tandem areprovided with marginal relays in their sleeve circuits. These marginalrelays are responsive to received signals and control the connection ofbattery with the talking conductors of the toll cord, therebyoriginating similar signals which be transmitted to the distant stationof the tandem toll line.

Further details of the apparatus may be descriptionof the operationthereof which is as follows:

Assuming that it is, desired to establish a long distance connectionbetween a local calling line at station M and a local called line atstation N, the plug PM of the toll cord TC at the station M will beinserted in the jack J of the toll switching trunk T associated with thecalling line, and the plug PM will be inserted OJ, of the toll line Ltending the connection oversaid line and sig naling the incomingoperator at station N. A circuit is thereby completed from ground, overthe sleeve contacts of jack J and plug PM and through the windings. ofrelay 12 and marginal relay 13 to battery. Relay 12 is energized toclose the talking conductors of the toll cord TC, but relay 13 ismarginal and does not respond to current flowing over A circuit is alsocompleted through the winding of marin the outgoing jack from battery,

ginal relay 14:, order the sleeve contacts of plug PM and'jack 01L,through the winding of relay 15, upper back contact of said relay,through resistance 16 and over the back left hand contact of relay 17 toground. Relay 14 is marginal and is not energized by current flowingover this circuit, butrela 1 Kris energized and completes at its upperfront contact, a locking circuit over the sleeve cir-' for the purposeof eX- at its front left hand contact completes a circuit from groundthrough the winding of relay 19 to battery. Relay 19 upon beingenergized completes a circuit from battery, over its left hand frontcontact and over the dotted line conductor 20, through the various busysignals (not shown) associated with the toll line to ground. The othercircuit changes incident to the energization of relay 19 are withouteffect at this time. Relay 17 by shifting its middle armature from itsback to its front contact momentarily opens the locking circuit of relay21, said circuit being traced as follows: from ground, right hand frontcontact and winding of relay 21, middle back contact of relay 17, backcontact of relay 23, left hand back contact of relay relay 23, frontcontact of relay 1?, left hand back contact of relay 21, over conductorB and through the winding of relay G and the left hand winding of relayH from which point the circuit may be completed in several differentways depending on the conditions then existing. Assuming the circuits tobe in the condition they would present in case no line had previouslytransmitted a signal, the circuit would be completed from the winding ofrelay H over its left hand back contact, over the extreme right handback contact of relay G over the left hand back contact of relay H, overthe back contact of relay 26, through the winding of re: lay 27 and overthe back ever, some one of the H relays would be locked up in serieswith the right hand wind ing of relay 26, over the back contact of relay27, due to the fact that the winding of relay 27 and over the backcontact of relay. 28 to battery. Relays 27, H and G, will, therefore, beenergized over some one of their possible circuits, providing that no Grelay is at that time energized due to some other line being engaged intransmitting a signal. Relay 27 upon being energized completes acircuitover its front concontact of relay 28 to ground. Under normalconditions, how

a signal had been transmitted by the line with which that par-,

tact, through the two windings of relay 26 in series, maintaining saidrelay energized. The energization of relay 27, at the same time, byopening its back contact breaks the locking circuit for the left handwinding of any H relay, such as H which had been previously locked up.Relays G, and H are now locked up over a circuit from battery, over theinner right hand front contact of relay G through the winding of saidrelay and through the left hand winding of relay H and thence over thecircuit previously traced to ground, at the back contact of relay 28.Upon the energization of relays G, and H, a circuit is also completed asfollows: from ground, back contact of relay 28, through the winding ofrelay 27, over the front left hand contact of relay H front extremeright hand contact of relay G over the conductor A, over the back righthand Contact of relay 21, through winding of said relav. over the frontmiddle contact of relay l7 and thence over the circuit previously tracedto battery, at the back contact of relay 25. Relay 21 is again energizedand locked up by the circuit thus completed.

Before proceeding with the translating operations resulting from theenergi,zation of relay G the manner in which the order of transmissionof signals from different lines is determined will be described.vAssuming that while line L has control of the circuit signals should beinitiated by lines L and L the G and H relays of said lines cannot beoperated for the reason that the ground connections from the left handwindings of the H relays of said lines extend over the extreme righthand contact of relay G which contact is now opened. When the signalinitiated by line L has been transmitted, the relay 28 will beenergized, as hereinafter described, thereby de-energizing relay G and27. The de-energization of relay 27 closes a locking circuit from theright hand winding of the relay H over the front right hand contactthereof, over the back contact of relay 27 and through the right handwinding of relay 26 to ground, thereby maintaining relaysH and 26energized. Relays G and H of line L will now be energized in preferenceto relays G, and H, for the reason that the ground connection for relaysH and G must pass over the extreme right hand contact of relay G, whichupon energizing will hold open the circuit for relays G and H lhecircuit for relays G and H will be completed through the winding ofrelay G left hand winding of relay H extreme right hand back contact ofrelay G left hand front contact of relay H throughthe winding of relay27, over the back contact of relay 28 to ground. Relay 27 is nowenergized and completes a circuit for the relay 26, through its twowindings in series,

at the same time opening the locking circuit through the right handwinding of relay H,, which is accordingly de-energized. The energizationcircuit for relays G and H would have to extend from the left handwinding of relay H over the left hand back contact of said relay, frontcontact of relay 26 and over the right hand contact of relay G over thefront left hand contact of relay H to the winding of relay 27, over theback contact of relay 28 to ground. It will be seen, therefore, thatline L has the preference. Assuming now that while line L is signaling,a new signal has been originated on line L in addition to the signalwaiting on line L,, as soon as the signal for line L is transmittedrelay 28 opens a circuit of relay 27 and relay G and the relay H remainslocked up through its right hand winding in series with the right handwinding of relay 26. Line L now has preference over line L, since thecircuit of its relays G, and H as previously traced, will not be heldopen at any contact, whereas the circuit for relays G and H mustpass-over the right hand contact of relay G which will be held open assoon as relay G is energized. The circuit for relays G, and H will be asfollows: from battery, through the left hand winding of relay H over theleft hand back contact of said relay, over the extreme right handcontact of relay G which will now be opened, over the front left handcontact of relay H which is now energized, and thence through thewinding of relay 27 and over the circuit previously traced to ground.Assuming now that while the signal originated by line L is beingtransmitted. a signal is originated on line L in addition to thatwaiting upon the line L upon the completion of the transmission of thesignal of the line L relay 28 is energized and opens a circuit of relays27 and G thereby locking the relay H through its right hand winding. Theline L now has preference over the line L since the circuit just tracedfor relays G and H will be completed while the circuit for the relays Gand of the line L will be held open at the right hand contact of relay GIt will thus be seen that the G and H relays of the various lines arearranged in an endless chain, with the H relay of the line whichtransmitted the last signal always locked up so that a plurality ofsignals simultaneously waiting upon other lines will be transmitted inregular order beginning with the nearest line on the left of the G and Hrelays which transmitted the last signal.

Returning now to the translating operations incident to the energizationof the relay Gr resulting from the insertion of the plug PM in the jackOJ it will be observed that at its inner left hand contact said relaycon- 130 nects ground through the right hand winding of relay 4, therebyenergizing said relay.

elay G over its remaining left hand contacts controls circuits forrelays 1 and 6, but since these circuits extend over conductors C and D,which are opened at this time, circuits for relays 1 and 6 are notclosed. As soon as relay 4 is energized it completes a locking circuitthrough its hand winding and over its left hand contact, through thewinding of relay 29, and over the back contact of relay 30 to ground.Relay 29 is now energized and completes a circuit from ground, over theinner ring 31, through segment 32 of the transmitting distributor TD,over the front contact of relay 29 and through the windings of startmagnet 34 to battery. The brusharm of the distributor is now re leasedand in passing from the segment 7 to the segment .9 transmits a negativeimpulse over the signaling path P from the segment a, brush and ring 35of the distributor, over the path P and through the winding of thepolarized relay 36 at station N to ground. Previous to the transmissionof thisnegative impulse positive current was flowing over the path Pfrom the segment r of the distributor TD thereby holding the armature ofthe polarized relay 36 upon its upper contact. Upon receiving thenegative starting impulse, however, the lower contact of the polarizedrelav is closed and a circuit is completed from ground, over saidcontact, over segment 37, brush and segment 38 of the receivingdistributor RD at station N and through the winding of the start magnet39 of said distributor to battery. The brush arm of the receivingdistributor is now released and rotates in a clockwise direction.

It will be noted that as the brusharm of the transmitting distributor TDrotates over the segments 1 to 6, impulses are transmitted over the pathP, whose polarity depends upon the conditions of relays 1 to 6. It willbe remembered that relay 4 was energized so that the transmittingdistributor now transmits a code combination consisting of threenegative impulses, one positive impulse and two additional negativeimpulses. These im+ pulses are received at the station N as the brusharmof the receiving distributor RD is passing over the segments 11, 22',33, and so forth. During the negative impulses the armature of thepolarized relay is resting upon its lower contact and no circuit changesresult from these impulses. When the fourth or positive impulse of thecode combination is received, the brush of the dis tributor is passingover segment 44 and a circuit is completed from ground, over the uppercontact of polarized relay 36, segment 40 of receiving distributor RD,brush and segment 44 of said distributor and through the windings ofrelay 44 to battery. Relay 44 is locked up over its front contact andover the back contact of relay 41. Relay 44' also closes a circuit frombattery, through the winding of pyramid relay 42, over the front contactof relay 44 and over the back contact of relay 41 to ground. Just afterreceiving the last impulse of the code combination, the brusharm of thedistributor passes over segments 47 and 48, thereby completing a circuitfrom negative battery, over the left hand back contact of relay 66, oversegments 47 and 48, left hand back contact ofrelay 55, left hand frontcon.- tact of relay 42, right hand back contact of relay 43, middle backcontact of relay 45, right hand back contact of relay 46, over theconductor F and through the left hand winding of relay 49 to ground.Before coming to rest the brusharm of the distributor RD closes acircuit from ground, over segments 95 and 96 and through the winding ofrelay 41 to battery. Relay 4]. is thereby energized and by opening itsback contact breaks the locking circuit of relay 44, thereby restoringthe pyramid relays to normal.

Relay 49 is energized over the circuit above traced and at its righthand front contact completesv a locking circuit through its right handwinding. At its extreme left hand contact a circuit is prepared forrelay 50 and at its inner left hand front contact a circuit is completedfrom ground, over said contact, over the left hand back contact of relay51, right hand back contact of relay 52, inner right hand back contactof relay 58, through lamp 54 associated with the answering jack AJ, atthe incoming operators position and over the right hand back contact ofrelay 56 to battery. The lamp 54 is now caused to glow thereby apprisingthe toll operator at station N that a calling line has been connected tothe toll line L The operator thereupon inserts the plug PN of the tollcord TC into the jack AJ, thereby completing a. circuit from battery,through the winding of marginal relay 57, sleeve contacts of the plugand ack, through the winding of relay 56 and over the back contact ofrelay 58 to ground. Relay 56 is energized over the circuit thus traced,but relay 57 is marginal and does not pull up its armature. Theenergization of relay 56 at its extreme left hand front con-tact closesa circuit from ground, over said contact and through the windings ofrelay 59 to battery. Relay 59 is energized to hold open the circuit ofthe ringing responsive relay 60 and also to hold open a circuit of therelay 58 so that it can not be energized bythe operator inadvertentlyinserting a plug in one of the outgoing jacks associated with the tollline L at the station N. Relay 56 at its right hand contact opens acircuit previously traced for the lamp 54, extinguishing said lamp andat its front right hand contact completes a circuit from battery, overthe dotted conductor 61 and through busy signals (not shown) associatedwith the toll line L at various terminal positions and thence to ground.A circuit is also completed over the front right hand contact of relay56, from battery, through the winding of relay 62, over the left handcontact of relay 68 and over the right hand front contact of relay 49 toground. Relay 62 is now energized but produces no effective results atthis time.

The toll operator at station N also inserts the plug PN of the toll cordTC into the jack J of the toll switching trunk T, over which theconnection is extended by the B operator to the called subscribers line.This operation results in the energization of sleeve relay 64s butsleeve relay 65 is marginal and is not actuated. The energization ofrelay 64c closes the tal ing conductors of the toll cord. As soon 3 theconnection is completed to the called subscribers line over the tollswitching trunk T, the called subscribers receiver being on the switchhook, battery is bridged across the talking conductors of the tollswitching trunk in a manner well known in theart, thereby completing acircuit over the tip and ring conductors of the jack J and the plug PN,over the contact of relay 64: and the normal contacts of the ringing key67, through the upper and middle windings of the triple wound relay 68,over the conductors 69 of the toll cord, over the contacts of thesplitting key 7 O and ringing key 71, tip and ring contacts of the plugPN and jack AJ over the normal contacts of the ringing relay 72 and overthe left hand front contact of relay 4:9 to the winding of relay 50.Relay 50 and the triple wound relay 68 are energized over the circuitthus traced and relay 68 is locked up from battery, through its lowerwinding and over its lower front contact and over the lower frontcontact of relay 64 to ground. A circuit is also completed from groundover the lower front contact of relay 64, over the lower front contactof relay 68 and through the winding of relay 73 to battery. Relay 73upon being energized automatically disconnects the operators set fromthe toll cord and at its outer front contacts completes a talkingconnection over conductors 7 4: of the toll cord, thereby shortcircuiting the upper windings of relay 68 and the condensers andcontacts of the splitting key 70. The toll operator now has no furthercontrol over the connection except to take it down in response to adisconnect signal. The above circuit changes also eliminate transmissionlosses due to the contacts of the splitting key, the windings of therelay 68 and the condensers.

The energization of the relay 50. upon the completion of the connectionto the called. subscribers line, closes a circuit from battery over thelower front contact of said relay and through the winding of slowrelease relay 75 to ground. Relay 75 in shiftingv its right handarmature from its back to its front contact momentarily opens thecircuit of locking relay 76, which might have been traced from battery,over the back contact of relay 77, right hand back contact of relay 75,back contact of relay 60, middle back contact of relay 58 and throughthe winding and over the front left hand contact of relay 7 6 to ground.Relay 76 is now de-enen gized and a circuit is thereby completed frombattery over the upper front contact of relay 50, right hand frontcontact of relay 75, back contact of relay 60, middle back contact ofrelay 58, right hand back contact of relay 76, over the conductor B, andassuming that no signal is being transmitted from any other line,through the winding of relay G and the right hand winding of relay Hover a path, depending upon the condition of the lockout circuit at thistime, through the winding of relay 78 and over the back contact of relay79 to ground. The lock-out function of G and H relays at station N isexactly the same as that at station M and need not be further described.Relay G, upon being energized completes a locking circuit from battery,over its inner left hand front contact, thereby locking up said relayand the relay H At its extreme left hand front contact relay G, closes acircuit from ground, over the back contact of relay 79, winding of relay78, right hand contact of relay H,,-left hand contact of relay G overconductor A, left hand back contact and winding of relay 76, middle backcontact of relay 58 and thence over a circuit previously traced tobattery at the upper front contact of relay 50. Relay 76 is againenergized and locked up. At its inner right hand contact relay G,connects ground through the left hand winding of relay t to battery,thereby energizing said relay. The remaining right hand contacts ofrelay G, control circuits of relay 1 and 6. These circuits are opened atthis time and hence these relays are unenergized.

As soon as the relay 4 is energized a locking circuit is completedthrough its right hand winding and over its right hand front contact,through the winding of relay 79 and over the back contact of relay 80 toground. Relay 79 closes a circuit of the start magnet 81 of thetransmitting distributor TD, thereby releasing the brusharm of thedistributor, which now transmits over the signaling path P a negativestarting impulse followed by a code combination CODSlStlIlg of threenegative impulses, one positive impulse and two additional negativeimpulses, the positive impulse being due to the energization of relay l.The starting impulse transmitted over the path P, acting upon thepolarized relay 82 at station M, re-

sults in the energization of the start magnet 83 of the receivingdistributor RD at station M. The brusharm of the distributor upon beingreleased rotates in a counter clockwise direction over the varioussegments and in response to the positive impulse transmitted over thepath P completes a circuit from battery through the Winding of relay 44,over the segments 44 and 84 of the distributor and over the uppercontact of polarized relay 82 to ground. An instant after the codecombination has been received, the brusharm, in passing over segments 85and 86 of the distributor, completes a circuit from negative battery,over the right hand back contact of relay 66, segments 85 and 86, righthand back contact of relay 55, front right hand contact of pyramid relay87, which was energized. by relay 44, back left hand contact of relay88, middle back contact of pyramid relay 89, left hand back contact ofpyramid relay 90, over conductor F and through the right hand winding ofrelay 91 to ground. The brusharm of the distributor just before comingto rest completes a circuit from ground, over segments 92 and 93,through the winding of relay 94, which by opening its right hand backcontact breaks the locking circuit of relay 44 and restores the pyramidrelay circuit to normal.

The energization of relay 91, over the circuit traced through its righthand winding, results in preparing a circuit for the relay 97, over theextreme right hand front contact of relay 91. Relay 97 and the triplewound relay 98 of the toll cord TC are not energized, however, asbattery is disconnected fronr the toll switching trunk T due to the factthat the calling subscriber has his receiver removed from the switchhook. Relay 91 at its left hand front contact completes a lockingcircuit through its left hand winding and also completes a circuit fromground over said contact, over the back right hand contact of relay 99,through the Winding of slow release relay 100 and over the front lefthand contact of relay 19 to battery, thus energizing relay 100. At itsinner right hand front contact relay 91 completes a circuit from ground,over the right hand back contact of relay 101, left hand back contact ofrelay 102, middle front contact of relay 19, back con tact of relay 103,through resistance 104, lower front cont-act of relay 15 and over thesleeve conductors ofplug PM and jack OJ, and through the winding ofmarginal relay 14 to battery. The completion of the circuit above tracedin shunt with the winding of the relay 15 decreases the resistance ofthe sleeve circuit sufiiciently to operate the marginal relay 14, whichis now energized to complete the circuit of the lamp 105.

The glowing of lamp 105 indicates to the toll operator at station M thatthe connection has been completed to the called sub scriber and his lineis now ready to be rung. The toll operator therefore actuates theringing key 106 ofthe toll cord TC and applies ringing current over thetip and ring conductors of the line L through the left hand windings ofthe transformer 107 and over the back right hand contact of relay 18 tothe winding of ringing responsive relay 23. Relay 23 by opening itsright hand con- 76 tact breaks the locking circuit of relay 21, which(it will be remembered) passed over said contact. As soon as the ringingcurrent ceases and the relay 23 is again deenergized, a circuit Will becompleted from battery, over the back contact of relay 25, left handback contact of relay 24, back contact of relay 23, middle front contactof relay 17, back contact of relay 21 and over the conductor B andthrough the winding of relay G and the left hand winding of relay H toground at the back' contact of relay 28. Relay G upon being energizedagain locks up the relay 21 over the conductor A and at its inner lefthand contact closes a circuit for the relay 4, thereby setting thetransmitter TD into operation to transmit over the path P a startingimpulse followed by the same code combination as was transmitted before;viz., three negative impulses, a positive and two additional negativeimpulses. The receiving distributor RD at station N is thereforereleased and in response to this code combination again transmits anegative impulse from negative battery, over the back left hand contactof relay 66, segments 47 and 48 of the distributor, left hand contact ofrelay 55, left hand front contact of relay 42, right hand back contactof relay 43, middle back contact of relay 45, right hand back contact ofrelay 46, over the conductor F and through the left hand winding ofrelay 49 in parallel with a circuit through the left hand Winding ofrelay 63 and over the right hand front con- 110 tact of relay 62 toground. Relay 49 being already locked up, no effect was produced by thisimpulse upon said relay. Relay 63 is energized and completes a circuitfrom bat tery through the left hand front contact of relay 62 to ground.At its left hand front contact relay 63 completes a circuit from ground,over the right hand front contact of relay 49, left hand front contactofrelay 63 and through the winding of slow release relayl08 to battery.Relay 108'conipletes a circuit from ground over its front contact, overthe back left hand contact of relay 53 and thence in parallel throughthe windings of relays 72 and 77 to battery. Relay 72-is 12b maintainedenergized for a brief period dur ing which the slow release relay 62 isdeenergized by the opening of its circuit at the left hand contactof'relay 63, thereby unlocking relay 63 which releases and in 1:0

turn causes the de-energization of relay 108. These relays aresuriiciently slow acting, however, to maintain the relay 72 energizedfor a period suificiently long to perform the ringing operation. Theactuation of relay 72 in applying ringing current over the toll cord TCand the toll switching trunk T to the called subscribers line opens thecircuit of the relay 50 which in turn causes the deenergization of relay75. In order to prevent the opening of the locking circuit of therelay76, due to this operation, the actuation of relay 77 completes anadditional locking circuit for said relay 76, from battery, over thefront contact of relay 77, over the back contact of relay 60, middleback contact of relay 58 through the winding of relay 76 and its lefthand front contact to ground.

When the called subscriber responds to the ringing signal thustransmitted, battery is disconnected from the talking conductors of thetoll. switching trunk T, in a manner well known in the art, therebycausing the de-energization of the relay 50, which, assuming that therelay 77 has been de-energized at the completion of the ringingoperation, opens at the upper contact of said relay 50 a locking circuitof the relay 76, which is de-energized, thereby completing a circuitfrom battery, over the back con tact of relay 77, back right handcontact of relay 75, back contact of relay 60, middle back contact ofrelay 58, back contact of relay 76, over the conductor 13, through thewinding of relay G and the right hand winding of relay H, to ground atthe back contact of relay 7 9. Relay G, upon being energized completes acircuit over the conductor A to again lock up the relay 76 and at itsinner right hand front contact connects ground through the left handwinding of relay st to energize said relay. At its outer right handfront contact relay G, completes a circuit for the relay 6 as follows:from ground over the left hand back contact of relay 7 5, extreme lefthand back contact of relay 58, conductor C, outer right hand contact ofrelay G and through the left hand winding of relay 6 to battery. Relays4 and 6 are now locked up and release the brusharm of the distributor TDto transmit a starting impulse followed by a code combination consistingof three negative impulses, a positive impulse, another negative and afinal positive impulse.

At station M the receiving distributor RD is set into operation by thestarting impulse and in response to the code combination relays 4:4 and66 are energized and locked up so that a momentary circuit is closedfrom positive battery, over the front right hand contact of relay 66,segments 85 and 86, back right hand contact of relay 55, front righthand contact of relay 87, back left hand contact of relay 88, backmiddle contact of relay 89, back left hand contact of relay 90 and overthe conductor F, through the right hand winding of relay 91. The impulsethus caused to flow through the right hand winding of relay 91 is ofsuch a direction as to cause a differential action between the twowindings of said relay so that said relay is de-energized, therebyopening at its left hand contact a circuit previously traced for relay100, which is now (lo-energized. At its inner right hand contact relay91, upon being de-energized opens the shunt circuit )reviously traced.through resistance 104i, about the winding of relay 15, so that manginal relay 1% no longer receives sufficient current to energize itswinding and the lamp 105 is extin uished to indicate to the tolloperator at station M that the called subscriber has answered.

Should the called subscriber desire to attract the attention of the tolloperator at station M by flashing his switch hook, the relay 50 of thetoll line L, will be intermittently energized and (lo-energized in response to the flashing of the switch hook, which intermittently connectsbattery to the talking conductors of the toll switching trunk T. Relay50 at its lower front contact sends a succession of impulses through thewinding of slow release relay which is maintained energized during theflashing of the switch hook. Relay 50 in moving its upper armature fromits front contact while relay 75 is energized, momentarily opens thecircuit of locking relay 76, which is thereby de-energized, and acircuit is com pleted from battery, over the upper front cont-act ofrelay 50, right hand front contact of relay 75, back contact of relay60, middle back contact of relay 58, back contact of relay 76, over theconductor B and through the winding of relay G and right hand winding ofrelay H, to ground at the back contact of relay 79. -Relay G upon beingenergized is locked up and at its front left hand contact completes acircuit over conductor A to again energize and lock up the relay 7 6.The circuit for the relay 76, however, it will be noted, passes over theupper ront contact of relay 50, which is intermittently closed inresponse to the flashing of the switch hook. Consequently, the relay 76will continue to be intermittently de-energized to transmit a successionof recall signals as often as it is able to obtain control of thelook-out circuit between periods when other lines are transmittingsignals. The energization of the relay G, at its inner right hand frontcontact completes a circuit for the relay 4;. The circuit over conductorG controlled by the outer right hand contact of relay G is held open atthe left hand contact of relay 7 5 and a circuit for conductor D is alsoopened. Consequently, relays 1 and 6 are not actuated. Relay 4 uponbeing energized and locked up releases the transmitting distributor TDto transmit a starting impulse followed by a code combination of threenegative impulses, one positive and two additional negative impulseseach time the line L, obtains control of the distributor TD during theflashing operation At station M distributor RD is released by thestarting impulse and in response to the fourth, or positive impulse,causes the relay 4A to be energized and lockedup, there by completing acircuit for the relay 87. A negative impulse is now transmitted fromnegative battery, over the back right hand contact of relay 66, oversegments 85 and 86, right hand back contact of relay 55, front righthand contact of relay 87, back left hand contact of relay 88, middleback contact of relay 89, left-hand back contact of relay 90, overconductor F and through the right hand winding of relay 91 to ground.Relay 91 is again locked up as before and completes a circuit throughits left hand front contact to energize the relay 100. At its innerright hand contact relay 91 again closes the shunt circuit throughresistance 104, about the winding of relay 15, to cause the marginalrelay 14 to be energized, thereby completing a circuit for the lamp 105.I

As previously stated, however, due to the intermittent closing of theupper contact of relay 50, the same signal is successively repeated bythe relay G, and fl, and the same code combination will again betransmitted over the signaling path P. lVhen the receiving distributor,in response to the retransmission of this code combination, sends asecond negative impulse over the conductor F, said impulse, in additionto tlmving through the right hand windings of relay J1, also flowsthrough the right hand winding of relay 99 and over the left hand frontcontact of relay 100-to ground. lie lay 99 is locked up and at its lefthand front contact completes a circuit from ground, over the left handfront contact of relay 91, over the right hand front contact of relay99, through the winding of relay 109 to battery. At the same time thatthis circuit is closed through the relay 99, the circuit previouslytraced through the relay 100 is opened and after an interval this relayis (lo-energized thereby opening a circuit of relay 109 which, after anadditional interval, will also be (lo-energized. The total time for thisoperation is considerable, however, and during this period a circuit iscompleted over the front contact of relay 109, front right hand contactof relay 19, through the winding of relay 103 to battery. Relay 103 uponbein thus energized completes a circuit from ground through interrupter110, front contact of relay 103, through resistance 10% to the sleevecontacts of plug PM and jack OJ thereby intermittently shunting thewinding of relay 15 to intermittently energize relay 1 1. This causesthe lamp 105 to flash. The operations just described will continue atintervals so long as the called subscriber continues to flash his switchhook, thereby indicating to the toll operator at station M that thecalled subscriber desires her' circuit of locking relay 21 which isthereby de-energized. A circuit is now closed from battery over the backcontact of relay 25,

left hand back contact of relay 2 1, right hand back contact of relay23, middle back contact of relay 1?, left hand back contact of relay 21,over the conductor B, through the winding of relay G, and left handwinding of relay H, to ground, at the back contact 'of relay 28. RelayG, at its outer right hand contact aga'n locks up the relay 21, over theconductor A. At its inner left hand contact relay G1, completes acircuit for the relay l, which is energized and locked up; while at itsouter left hand contact relay G completes a circuit from ground, overthe back right hand contact of relay 2%, the outer right hand. backcontact of relay l'i, over the conductor O, the outermost left handcontact of relay G through the'right hand winding of relay 6 to battery.Relay 6 is also energized and locked up. As soon as relays 4- and 6 areenergized and locked up, thetransmit ting distributor TD is set intooperation to transmit a starting impulse followed by a code combination,consisting of three negative impulses, a positive, another negative anda final positive impulse.

At station Nthe receiving distributor RD is. now set into operation andin response to the code combination just transmitted, locks up relays44: and 66. A momentary circuit is consequently completed from positivebattery, over the front left hand contact of relay 66, segment l? and18, back left hand contact of relay 55, front left hand contact of relay152, back right hand contact of relay -13, middle back contact of relay45, right hand back contact of relay as, over the conductor F, throughthe lefthand winding of relay 5L9 to ground. This impulse is opposite insign to that which was previously transi lay 1s de-energized.

mitted through the left hand winding of relay 4E9 and, consequently,energizes said winding dilierentially with respect to the lockingwinding of said relay so that the re- The de-energization of relay &9closes a circuit in shunt with the winding of sleeve relay 56, fromground, over the back right hand contact of said relay, over the innerleft hand front contact 01 relay 56, through resistance 111. Thisdecreases the resistance over the sleeve contacts of jack AJ, and plugPN, thereby energizing marginal relay 57 to complete the circuit of thedisconnect lamp 112. The toll operator at station N, in response to thissig nal, withdraws the plugsPN and PN from the corresponding jacks. Thecircuit through relays 64 and 65 in series is thereby opened so that thelocking circuit through the lower winding of relay 6S and through thewinding of relay T3 is broken at the lower contact of relay (it, therebyrestoring the cord circuit to normal. The circuit of sleeve relay 56 isalso opened by withdrawing the plug PN from the jack, so that thevarious relays associated with the line L, at station N are restored tonormal.

Returning again to the situation existing after the toll operator atstation N, in response to the glowing oi the guard lamp 541 at theincoming operators position, had extended the connection from the tollline L over the toll cord TO to the toll switching trunk T, it will beremembered that a signal comprising a code combination of three negativeimpulses, one positive and two ad ditional negative impulses wastransmitted to the station M, thereby operating lamp 105 to indicatethat the called line is ready to be rung. In case the called subscribersline had been found. busy by the B operator, the toll switching trunkwould have been plugged into a busy back circuit, which would result inintermittently connecting battery to the talking conductors of theswitching trunk T in a manner analogous to that resulting "from theflashing oi the subscribers switch hook. As a result of this connection,the relay 50 would be intermittently energized to transmita successionof code combinations each comprising three negative impulses, a positiveand two negative impulses, in the same manner as already described inconnection with the flashing of the subscribers switch hook. At thestation M the relay 10b would be energized in response to asuccession 01these signals, thereby causing the fiashing of the lamp 105. This signalcoming before the signal indicating that the line is ready to be rung,indicates to the operator that the line is busy. The toll operator atstation M' is then tree to take down the connection it she so desires.

Where the operator at the incoming position at station N hasbeen unableto complete the connection to the called subscriber,either because thecalled subscriber is busy or for any other'reason is not available, itis desirable that she should be able upon obtaining access to the calledsubscribers line to establish the connection over the toll line in thereverse direction to the oliice at station M where the call originated,and in so doing should be able to signal the operator at the outgoingposition, since such operator will be familiar with the details of thecall. This result may be accomplished by inserting the plug Phi of thetoll cord TC into the outgoing jack 0J at the station N. This ope 'ationresults in completing a circuit from battery, through the winding ofmarginal relay 57,0ver the sleeve contacts of plug PN and jack OJ, atthe station N. This operation results in completing a circuit frombattery, through the winding of marginal. relay 5?, over the sleevecontacts 01 plug Plv and jack 0J through the winding of relay 113, overthe upper back contact or said relay, through resistance 1H and over theright hand back contact of re lay 58 to ground. lielay 57 being marginalis not energized over said circuit, but relay 1.1.3 is energized andlocked up over its up per :iront contact in series with the winding ofrelay 58, which is also energized. Relay 58 at its right hand ilirontcontact completes a circuit tor relay 53 which relay in turn, at itsright hand front contact connects battery to the busy signals (notshown) included in conductor (31. Relay 58 in transferring its middlearmaturefrom its back to its front contact nunncntarily opens thecircuit of the normally locked up relay 76. A circuit is now completedfrom battery over the back contact oi? relay 77, right hand back contactof relay 75, back contact of relay (it), middle front contact of relay58, right hand back contact of relay 76, over conductor B and throughthe winding of relay (3, and the right hand winding oiilrelay H, toground at the back contact of relay 79. Relays (i and. iii, are lockedup and the t'ormcr closes, at its outermost left hand nlront contact, acircuit over the conductor A to energize and again lock up relay 76. Itwill be noted that relay 113 is provided with two lower contacts whichconnect ground to conductors G and D, respectively. Accordingly, whenrelay G is energized it completes circuits over its three right handcontacts, through the windings of relays 1, l and 6, respec tively.These relays are energized and locked up, thereby releasing thetransmitting distributor TD to ltransmit a starting impulse tollowed bya code combination con sisting of a positive impulse, two negativeimpulses, another positive, another negative and a final positiveimpulse, v

At station M the receiving distributor RD is set'into operation by thestarting impulse and in response to the three positive impulses of thecode combination, energizes and locks up relays 11, 44 and 66. As aresult of this operation, a positive impulse is transmitted frompositive battery, over the front right hand contact of relay 66, oversegments 85 and 86, right hand back contact of relay 55, front righthand" contact of relay 87, back left hand contact of relay 88, middleback contact of relay 89, left hand front contact of relay 90'and overconductor E and through the windings of polarized relay 114 to ground.The armature of polar relay 114 now makes connection with its left handcontact, thereby completing a circuit from ground, through the righthand winding of relay 91, over the armature of polar relay 114, throughthe winding of slow release relay 102 to battery. Relay 91 is energizedand locked up through its left hand winding. Relay 102 is also energizedand locked up, the locking circuit being traced from battery, throughthe winding and right hand front contact of relay 102 and over the lefthand front contact of relay 91 to ground. A circuit is now completedfrom ground over the inner right hand front contact of relay 91, overthe back right hand contact of relay 101, left hand front contact ofrelay 102, through lamp 115 associated with the answering jack AJ at theoutgoing operators position and thence over the left hand back contactof relay 116 to battery. The toll operator at station M in response tothis signal inserts the plug PM in the jackriJ thereby energizing relay116 to open the circuit of the lamp 115 at its left hand contact andapply battery to the conductor 20 leading to the busy signals (notshown). The details in cident to the completion of the connection andthe various signals transmitted will be similar to those alreadydescribed and need .not be further considered.

lVhere the call, originating at one station, such as station M, is to becompleted over two or more toll lines in tandem, the toll operator atthe originating station M will insert the plug PM of the toll cord TC inthe jack J of the toll switching trunk connected to the callingsubscribers line and a plug PM of said toll cord into the outgoing jackOJ which results in the actuation of a signal at the through operatorsposition at station N, as will now be described. A circuit is completedfrom battery, through the winding of marginal relay 14, over the sleevecontact of the plug and jack, through the winding of relay 117,resistance 16, to ground over the back left hand contact of relay 17.Relay 117 is energized and locked up over its front contact in serieswith relay 17, which is thereby engaged to complete a circuit of relay19, as already described. Relay 1'? at its middle armature momentarilyopens a aircuit of locking relay 21, thereby completing a circuit overthe back left hand contact of said locking relay and the conductor 13for the relays G and TL. It will be noted that relay 117 is providedwith a lower contact whereby ground is connected to the conductor D.Consequently, relay G over its first and second left hand contactsconnects ground to relays 1 and 4, respectively, thereby energizing andlocking up said relays. The transmitting distributor TD is now re leasedto transmit a starting impulse followed by a code combination consistingof a positive impulse, two negative impulses, another positive impulseand two additional negative impulses. At station N the distributor RD isset into operation by the starting impulse and in response to thepositive impulses of the code combination transmitted, energizes andlocks up relays 11" and 44, which, in turn, complete circuits for thecorresponding pyramid relays. A negative impulse isnow transmittedfronrnegative battery, over the back left hand contact of relay 66,segments 47 and 48 of the distributor RD, back left hand contact ofrelay 55, front left hand contact of relay42, back right hand contact ofrelay 43, middle back contact of relay 45 and right hand front contactof relay 46, over conductor E and through the windings of polar relay 118 to ground. Polar relay 118 in response to this impulse shifts itsarmature into connection with its left contact thereby conipleting acircuit lrom ground, through the left hand winding of relay 49, over theleft hand contactof relay 118 through the windings of slow releaserelay. 51 to battery. Relay 49 is locked up over its right hand frontcontact and through its right hand winding. At its inner left handcontact relay 49 completes a locking circuit for relay 51, from ground,over the inner left hand contact of relay 49 and over the right handfront contact of relay 51, through the winding of said relay to battery.A circuit is now completed by the relay 51, from ground, over the innerleft hand front contact of re lay 49, over the front left hand contactof relay 51, through the lamp 119 associated with the answering jack AJ,at the through operators position and thence over the back right handcontact of relay 56 to battery.

The glowing of lamp 119 apprises the through operator that a callingsubscriber has been connected tothe toll. line L, and in response tosaid signal the through operator inserts the plug PN of the toll cord TCinto the ack AJ thereby completing a circuit through the winding ofsleeve relay 56 to open the circuit of the lamp 119 and apply battery tobusy signals (not' shown) in con ductor 61. The through operator alsoinserts the plug PN in the jack L of a toll line L, leading to anotherdistant station where the connection is to be still further extended orelse completed to a called subscribers line. The jack J may be anoutgoing jack, leading to an outgoing, incoming or through operatorsposition at the dis tant station as the service conditions require.Assumin g for simplicity that it leads to the incomingoperatorsposition, a circuit is completed from battery, through marginal relay 05and relay 6 1, over the sleeve contacts of the plug and jack to a sleeverelay 120 associated with the toll line L This relay operates in amanner similar to the relay 15 at station M to transmit a signal over apath, similar to the signaling path P, to the distant station.

lVhen the connection has been completed at the distant stat-ion, thecalled subscrib-ers receiver being upon the switch hook, a signal willbe transmitted over the signaling path to indicate this fact. Thissignal results in connectinga resistance 121, corresponding to theresistance 10-;l at station iii, in shunt with the resistance oil relay120, thereby energizing the marginal relay (S5. The circuit changesbringing about this re sult are similar to those already described inconnection with the call from station M to station N. Upon theenergization of relay (55, a circuit is completed from ground, over thefront contact of said relay and through the winding of relay 122 tobattery. Relay 122 at its extreme left hand front contact completes acircuit through the lower winding of the triple wound relay 8 inparallel with the winding oi? relay 73. Relays T3 and 08 are therebyenergized and operate to disconnect the operators set and to shortcircuit the splitting key 70, upper and middle indiugs of the relay 6Sand the condensers, thereby eliminating the through operator at stationN l'rom any Further duties in connection with the call except to take do\vn the connection in response to a d iseonnect signal. The energizationof relay 122 also bridges l'iattery across conductors (39 of the tollcord TC, thereby completing a circuit from baittery, over the contactsoi the splitting key 70, contacts of the ringing key 71, tip and ringcontacts of the plug PN and jack AL, contacts of ringing relay 72 andover the left hand contact of relay i9 to the winding of relay 50. Theenergization of relay 50 results in the transmission of a signal overthe signaling path 1, whereby resistance 10% is connected in shunt withthe windings of relay 117, in a manner similar to that already describedin connection with the relay 17 Accordingly, marginal relay 14: isenergized to complete circuit for the lamp 105, indieating to the tolloperator at station M that the distant called subscriber is to be rung.

The toll operator at station M now actuates the ringing key 106 andtransmits ringing current to the winding of ringing responsive relay 23.Relay 23 upon being actuated opens the circuit of locking relay 21,which is deenergized, and at the end of the ringing signal and upon thede-encrgization of relay 28 a circuit is completed from battery, overthe right hand back contact of relay 25, left hand back contact of relay2 1, righthand back contact of relay 23, mid.- dle i'ront contact ofrelay 17, left hand back contact of relay 21, over conductor B andthrough the winding of relay G the left hand winding of relay H, toground at the back contact of relay 28. ltwill be again noted thatground is connected over the lower front contact of relay 117 to theconductor D so that relay G upon being energized connects ground to rela1 and lrespectively. The energization and locking up of these relaysresults in the transmission of the same code combination as wastransmitted to actuate the guard lamp 115); viz., a positive impulse,two negative li1lpulses, another positive impulse and two additionalnegative impulses. As a result of the transmission of this codecombinatimi relays 11 and 4 1-. are energized, thereby transmitting anegative impulse from ne 'a tire battery, over the back left hand conte;- of relay (30, segments i? and id of distributor RD, back left handcontact of relay 55, i'ront left hand contact of relay 42, back righthand contact of relay l3, middle back contact of relay l5 and right handfront contact ot relay 4-1-6, over conductor E and 'hrough the windingsof polar relay 118 to ground. Polar relay 118 again shifts its armatureinto contact with its left hand contact. It will be remembered that therelay 19 was energized. and locked up in response to the negativeimpulse previously transmit ted through the polar relay 11S and that,consequently, a. circuit was completed from ground, over the right hand:iront contact of said relay 49 and over the back left hand contact ofrelayil'i, through the winding oi relay 62and over the right hand troutcontact of relay 56 to battery. Relay (3:! therefore energized at themoment the pres ent negative impulse is being received by the relay 118,thereby completing a circuit from ground, over the right hand rrontcontact of relay 62, through the left hand winding of relay 63, over theleft hand contact of polar relay 118 and through the windin of relay 51to battery. Relay 3 upon being energized completes a circuit tor therelay 108, over its left hand rout contact, at the same time opening acircuit of slow release relay 62. Relay 108 closes a circuit for theringing relay 72 and the relay 77 to apply ringing current over thecontacts of the relay 72 during the period of time that is required forthe slow releasing re lay 62 and 108 to be de-energized. Relay

